Since lithium ion secondary battery has high voltage and high capacity, it is widely used as power source for mobile phones, digital cameras, video cameras, laptop computers, electric cars, etc. A generally used lithium ion secondary battery uses a liquid electrolyte obtained by dissolving an electrolytic salt in a nonaqueous solvent. Since the nonaqueous solvent contains a large amount of flammable solvent, ensuring the safety has been desired.
In order to ensure the safety, an all-solid secondary battery whose elements are formed from a solid material (a positive electrode active material, a negative electrode active material, a solid electrolyte, etc.) was proposed without a nonaqueous solvent (JP2014-137869A:Patent Document 1, JP2014-212022A:Patent Document 2). The all-solid secondary battery comprises a positive electrode, a negative electrode and a solid electrolyte layer between the positive electrode and the negative electrode, all of which are made of a solid material. The positive electrode or the negative electrode of the all-solid secondary battery may comprise the solid electrolyte in order to improve the ionic conductivity of the interface between the positive electrode active material and the negative electrode active material which constitute the electrodes.
In Patent Document 1, a positive electrode, a negative electrode and a solid electrolyte layer are obtained by binding a solid material with a binder resin such as polyvinyl pyrrolidone and butylene rubber. Patent Document 2 proposes a technique of removing a binder resin used in producing constituent elements of the battery by a heat treatment from the viewpoint of preventing problems such as deterioration of the solid material due to the binder resin and internal short circuit due to the binder resin.